1. Field of the Invention
The present invention relates to a subsea wellhead assembly for an oil and gas well, and more particularly relates to a universal tubing hanger suspension assembly for use in a subsea wellhead assembly.
2. Description of the Related Art
A typical subsea wellhead assembly includes a wellhead housing installed at the sea floor. With a drilling blowout preventer (BOP) stack installed on the wellhead housing, the well bore is drilled while successively installing concentric casing strings in the well bore. Typically, each successive casing string is cemented at its lower end and includes a casing hanger sealed with a mechanical seal assembly at its upper end in the wellhead housing.
In order to produce the cased well, a production tubing string and tubing hanger is typically run into the well bore through the BOP stack and the tubing hanger is landed, sealed and locked in the wellhead housing and/or the casing hanger. Upon sealing the bore(s) extending through the tubing hanger, the BOP stack is removed and a Christmas tree is lowered onto the wellhead housing. A Christmas tree is an oilfield term understood to include the control valves and chokes assembled at the top of a well to control the flow of oil and gas. It is vitally important to the operation and safety of the well that the proper connections are remotely formed between the Christmas tree, the wellhead housing, and the tubing hanger.
In a conventional completed well system, the Christmas tree is connected to the top of the wellhead housing over the tubing hanger. The tubing hanger supports at least one production tubing string which extends into the well bore. The tubing hanger provides a production bore within the tubing string and a conduit that communicates with the annulus surrounding the tubing string and inside the innermost or production casing string. In addition, the tubing hanger comprises at least one vertical production bore for communicating fluid between the tubing string and a corresponding production bore in the Christmas tree, and typically at least one vertical annulus bore for communicating fluid between the tubing annulus and a corresponding annulus bore in the Christmas tree. The tubing hanger may additionally include one or more service and control conduits for communicating control fluids and well chemicals through the tubing hanger or electrical power to devices or positions located in or below the tubing hanger.
A tubing hanger conventionally is sealed and rigidly locked into the wellhead housing or component in which it is landed. In a well having a conventional Christmas tree, the tubing hanger is landed in the wellhead housing. The tubing hanger typically includes an integral locking mechanism which, when activated, secures the tubing hanger to the wellhead housing or a profile in the casing hanger. The locking mechanism ensures that any subsequent pressure from within the well acting on the tubing hanger will not cause the tubing hanger to lift from the wellhead housing thereby resulting in an unsafe condition.
There are a limited number of subsea wellhead equipment manufacturers worldwide. Currently, the primary manufacturers of subsea wellhead housings are ABB Vetco Gray, Cooper Cameron Corp., Dril-Quip, FMC and Kvaerner. Each of the primary manufacturers has its own proprietary wellhead housing and casing hanger designs, dimensions and details. Quite frequently, a well is completed on Manufacturer A's wellhead housing and casing hangers using a tubing hanger and/or Christmas tree from Manufacturer B. However, since Manufacturer A's housing and casing hanger design is proprietary, Manufacturer B may not be able to connect its Christmas tree to Manufacturer A's housing without a license from Manufacturer A at a fee in order to design Manufacturer B's equipment to properly interconnect and mate with Manufacturer A's wellhead housing and casing hanger. This results in a substantial amount of additional engineering and costs or additional equipment (such as a tubing spool) when electing to purchase Manufacturer B's equipment for use with Manufacturer A's wellhead housing. Since each wellhead housing/system manufacturer has multiple models of housings and casing hangers with different proprietary details, it is not practical or economical for other manufacturers to build up an inventory of equipment for installation on other manufacturers' wellhead equipment. In addition to the added costs, it also increases the delivery time which is often vitally important to the well owner.
It is desirable to have a subsea well completion system that is adapted for use with wellhead housings from all manufacturers. It is further desirable to have a tubing hanger assembly adapted for positioning in the wellhead housing independently of any proprietary details of the wellhead housing. It is further desirable to have a universal tubing hanger assembly that is adapted for use in a plurality of wellhead housings, and even more desirable to have a universal tubing hanger assembly adapted for use in wellhead housings of two or more manufacturers.